A series of binuclear ruthenium(II) arene benzil bis(benzoylhydrazone) complexes (1–6) of the common composition [(η⁶-arene)₂Ru₂(L)Cl₂] (arene = benzene or p-cymene; L = benzil bis(benzoylhydrazone derivatives)) have been synthesized. The synthesised complexes have been thoroughly characterised by elemental analysis, IR, NMR, UV-vis and ESI-MS spectral methods. The coordination of the binucleating ligand to each ruthenium centre through azomethine nitrogen and imidolate oxygen was confirmed by single crystal XRD, which indicates the presence of the pseudo octahedral geometry. All the complexes were carefully screened for their cytotoxicity against HeLa, MDA-MB-231 and Hep G2 cells under in vitro conditions. Interestingly, the complexes 4 and 6 exhibit higher cytotoxicity than cisplatin, with low IC₅₀ values against all screened cancer cell lines. Furthermore, the mode of cell death in MDA-MB-231 cells was assessed by AO-EB, Hoechst 33258 staining and a flow cytometry technique along with the comet assay. The result of western blot analysis suggests that complexes 4 and 6 were shown to induce apoptosis via the mitochondrial pathway by up-regulating p53 and Bax, and down-regulating Bcl-2.

Ruthenium complexes with bioactive ligands are becoming promising substitutes for platinum complexes due to their precise action against various cancers. In the present study, the synthesis of three new arene Ru(II) complexes containing new carbazole-based hydrazone ligands of general formula [(η⁶-benzene)Ru(L)Cl] (1–3; L = carbazolone benzhydrazone ligands), and their anticancer properties are described. The structural characterization of the ligands and their ruthenium complexes has been realized with the aid of elemental analysis, IR, UV-vis, NMR and HR-MS techniques. The molecular structures of all three complexes have been elucidated by single crystal X-ray crystallography and reveal the existence of pseudo-octahedral geometry around the ruthenium. The in vitro cancer cell growth inhibition property of the complexes against A549 (lung carcinoma), A2780 (ovarian adenocarcinoma) and non-cancerous 16HBE (human lung bronchial epithelium) cells were examined by MTT assay. All the complexes display good cytotoxicity towards both of these types of cancer cell compared to the standard drug cisplatin, with low IC₅₀ values. Remarkably, complex 3, which contains an electron-donating substituent, induces a significant reduction of viability in A2780 cells. The inhibition capacity of the complexes towards A2780 cells proliferation was further confirmed using 5-ethynyl-2-deoxyuridine (EdU) assay via minimal DNA synthesis. The result of the acridine orange-ethidium bromide (AO-EB) fluorescent staining assay establishes that the cytotoxicity of the complexes was mediated by apoptosis in cancer cells. Furthermore, flow cytometry using Annexin V-FITC/propidium iodide (PI) double staining determines the quantitative discrimination of early apoptosis by the externalization of phosphatidylserine. In addition, cell cycle distribution indicates that the complexes block the cell cycle progression in the S-phase. The outcome of our investigation shows the promising scope and potency of tailored arene ruthenium complexes for precise cancer chemotherapy beyond platinum drugs.

Convenient synthesis of a series of eight octahedral ruthenium(II) carbonyl complexes having the general molecular formula [Ru(L)(CO)Cl(AsPh₃)₂] (where HL = thiophene aldehyde benzhydrazone ligand) has been described. The substituted benzhydrazone ligands behave as monoanionic bidentate N and O donors (L) and coordinate to the ruthenium(II) ion via the azomethine nitrogen and deprotonated amide oxygen. The compositions of the complexes have been established by elemental analysis, spectral methods (FT-IR, UV-Vis, ¹H NMR) and X-ray crystallography. The crystal structure of two of the complexes, viz., [Ru(L1)(CO)Cl(AsPh₃)₂] (1) and [Ru(L5)(CO)Cl(AsPh₃)₂] (5) have been solved by single crystal X-ray crystallography and it indicates the presence of a distorted octahedral geometry in these complexes. The complexes were demonstrated as efficient catalysts for the one-pot conversion of various aldehydes to their corresponding primary amides using NH₂OH·HCl and NaHCO₃. The effects of solvent, base, reaction temperature and catalyst loading on the catalytic activity of the most active ruthenium(II) carbonyl benzhydrazone complex were also investigated.